1. Field of the Invention
The present invention relates to a blended brake booster having a hydraulic lock during a manual brake application.
2. Description of the Related Art
The present invention is of a type hydraulic brake boosters referred to as a “full-power” brake booster, of which the following U.S. Pat. Nos. are considered to be typical: 4,441,319; 4,490,977; 4,514,981; 4,665,701; 4,685,297; 4,704,867; 4,724,674; 5,526,731, 5,927,074, 6,606,859 and 7,354,116. In such brake boosters, an accumulator is charged with fluid pressure and selectively activated through movement of a control valve by an input member to present pressurized fluid to an actuation chamber that acts on an actuation piston and is directly supplied to a first set of wheel brakes. The pressurized fluid acts on the actuation piston in to develop a force for moving a power piston in a master cylinder that pressurizes operational fluid that is presented to a second set of wheel brakes to effect a brake application. The operational pressure that is developed in the master cylinder is proportional to the force applied to the actuation piston and inversely proportional to the cross-sectional area of the power piston in the master cylinder for a given force applied to an input member by an operator to move the control valve. The resulting travel of the input member and brake pedal is proportional to the travel of the actuation piston in the master cylinder. Conversely, the travel of the power piston in the master cylinder is also proportional to the displacement of the fluid in the brake system at any given pressure and inversely proportional to the cross-sectional area of the actuation piston. Thus, the travel of the input member and brake pedal is inversely proportional to the cross-sectional area of the actuation piston. Given these facts, when brake blending is implemented during a brake application with such prior art structure, a pulsation may be felt by an operator on the input pedal.